Closed-loop, RF-coupled implanted medical device

Abstract

The implantable, electrically operated medical device system comprises an implantable radio frequency (RF) receiver and an external RF transmitter. The receiver has a receiving antenna and electronic circuitry coupled to the receiving antenna and includes a microcontroller having an output, a non-volatile memory coupled to the microcontroller and an implanted, electrically and autonomously operated medical device is coupled to the output of the microcontroller. The external RF transmitter has a power source and a transmitting antenna. The receiver further includes circuitry coupled to the microcontroller for regulating the power transmitted by the transmitter, whereby, RF energy can be transmitted by the transmitter and coupled into the receiver and the level of RF energy transmitted by the transmitter is controlled by the circuitry. The transmitter is also used to: a) program into the memory of the implanted device (receiver) its operating values; b) start and stop delivery of medical therapy by the implanted device, c) interrogate the operating values of the implanted device, and d) interrogate physiological parameters which are measured by the implanted device.

I claim: 
     
       1. An implantable, closed-loop, electrically operated medical system comprising: (a) an implantable radio frequency (RF) receiver coupled to an implanted, electrically and autonomously operated medical device; and, (b) an external RF transmitter which is used to supply said implanted medical device with electrical power; said receiver having a RF power receiving antenna, electronic circuitry coupled to said receiving antenna and including means for converting said received RF power into a D.C. voltage, a microcontroller having output and input means, a non-volatile memory coupled to said microcontroller, high/low voltage sensing means coupled to said microcontroller, means for up-linking commands to said transmitter to decrease or leave as is, said transmitted RF power, said implanted medical device being coupled to said output means of said microcontroller; and said transmitter having a power source, a RF power transmitting antenna, means for detecting and decoding commands up-linked by said receiver, and means for regulating said transmitted RF power level in response to said up-linked signals whereby, RF energy or power can be transmitted by said transmitter and coupled into said receiver where it is used exclusively to power said implanted medical device and the level of RF power transmitted by said transmitter is controlled by the level of voltage detected by said high/low voltage sensing means of said receiver. 
     
     
       2. The medical system of claim 1 wherein said electronic circuitry includes a rectifier coupled between said receiving antenna and said microcontroller. 
     
     
       3. The medical system of claim 2 wherein a positive DC output of said rectifier is coupled to a storage capacitor and the voltage level at said storage capacitor becomes a VCC supply voltage for said receiver. 
     
     
       4. The medical system of claim 1 wherein said electronic circuitry includes a multiplexer coupled between said microcontroller and the implanted medical device. 
     
     
       5. The medical system of claim 1 wherein said electronic circuitry includes a D/A converter coupled between said microcontroller and the implanted medical device, said D/A converter being capable of deliverinq stimulus pulses having either a constant current or a constant voltage. 
     
     
       6. The medical system of claim 1 wherein said electronic circuitry includes an A/D converter coupled between the implanted medical device and said microcontroller. 
     
     
       7. The medical system of claim 1 wherein said means for up-linking commands includes up-link circuitry coupled to said microcontroller for up-linking data to said transmitter. 
     
     
       8. The medical system of claim 1 wherein said transmitter includes a second microcontroller and down-link circuitry coupled to said second microcontroller for down-linking data to said receiver. 
     
     
       9. The medical system of claim 1 wherein said non-volatile memory is an erasable, reprogrammable non-volatile memory. 
     
     
       10. The medical system of claim 1 wherein microcontroller has an A/D input and said high/low voltage sensing means comprise a voltage divider defined by two resistors and a junction between said two resistors coupled to said A/D input of said microcontroller for sensing a voltage at the junction which is related to a supply voltage named VCC, said microcontroller using the voltage sensed by said voltage divider to cause said microcontroller to send, an increase, or a leave as is, signal to said transmitter. 
     
     
       11. The medical system of claim 1 wherein said transmitter comprises means for: (a) programming into said non-volatile memory operating values for controlling the functions of said implanted medical device; (b) starting and stopping delivery of medical therapy by said implanted medical device, and (c) interrogating said medical device to determine the actual operating values of said medical device. 
     
     
       12. The medical system of claim 1 wherein, when new operating values are programmed into said receiver by said transmitter, said operating values are automatically stored in said non-volatile memory, so that if transmission of RF power ceases and later is restored, said implanted medical device can resume operation at the previous values without reprogramming. 
     
     
       13. The medical system of claim 1 wherein said implanted medical device is a neural stimulator. 
     
     
       14. The medical system of claim 1 wherein said implanted medical device is a cardiac pacemaker. 
     
     
       15. The medical system of claim 1 wherein said high/low voltage sensing means comprise first and second comparators for sensing an upper voltage related to a supply voltage named VCC, and a lower voltage related to the supply voltage, VCC, and comparing those voltages with a reference voltage and then causing the microcontroller to send, an increase, or a leave as is, signal to said transmitter. 
     
     
       16. The medical device of claim 1 wherein said microcontroller in said receiver includes an A/D converter input for measuring and comparing a supply voltage, VCC against at least two predetermined thresholds, said VCC voltage representing the level of RF power reaching said receiver. 
     
     
       17. The medical device of claim 1 wherein said microcontroller is coupled to an inductor for up-linking signals to said transmitter for increasing or leaving as is said transmitted RF power level. 
     
     
       18. The medical device of claim 1 wherein said transmitter includes control means responsive to said up-link signals to decrease, maintain or increase the level of transmitted RF power. 
     
     
       19. The medical system of claim 1 wherein said implanted medical device comprises (a) an insulated lead having at least two conductors each connecting contacts between its proximal and distal ends, and (b) the contacts at the distal end forming electrodes used for electrical stimulation of adjacent tissue. 
     
     
       20. The medical system of claim 19 wherein said electronic circuitry further includes (a) means for measuring the voltage which develops at said electrodes during delivery of said electrical stimulus pulses of a known constant current value, said means for measuring voltage having an output signal connected to said microcontroller; and (b) means for calculating the electrode impedance by dividing the voltage sensed over a known constant current value. 
     
     
       21. The medical system of claim 1 wherein said receiver, in response to said received level of RF power, up-links signals to said transmitter to cause the level of transmitted RF power to be (a) decreased, (b) maintained, or (c) increased in the absence of any up-link signal, so that transmitted RF power is a function of received RF power; said transmitter and said receiver forming a closed-loop, auto-regulated RF power system for optimizing the life of a battery in said transmitter by maintaining transmitted RF power at the minimum level necessary for dependable and effective receiver operation, regardless of the operating values programmed into said medical device. 
     
     
       22. An implantable medical device system comprising an implantable medical device, an implantable receiver coupled to and associated with said medical device and a transmitter; said transmitter having means for transmitting a burst of RF energy to said implanted receiver;   said transmitter having means for receiving information from said implanted receiver;   said receiver having means for receiving said RF burst of energy from said transmitter and for using said burst of energy to supply an electrical signal to said implanted medical device;   means for transmitting to said transmitter information regarding the amount of RF energy needed to supply adequate power to said receiver and means in said transmitter for adjusting the amount of RF energy transmitted to said receiver depending upon said information received from said receiver.   
     
     
       23. The implantable medical system of claim 22 wherein said receiver includes means for determining if the power supplied to said receiver is sufficient to operate the receiver circuitry dependent upon the needs of the patient and means for transmitting to the transmitter information regarding whether or not the transmitted RF power received should be increased or decreased or stay the same. 
     
     
       24. The medical system of claim 22 wherein said transmitter includes means for adjusting the amplitude of a pulse of RF energy transmitted in response to said information received from said receiver thereby to increase or decrease the RF energy transmitted from said transmitter to said receiver. 
     
     
       25. The medical system of claim 22 wherein said transmitter includes means for adjusting the duration of a pulse of RF energy transmitted in response to said information received from said receiver thereby to increase or decrease the RF energy transmitted from said transmitter to said receiver.